The invention relates to a medical instrument, comprising a shaft, and a tool which is mounted on a distal end of the shaft in such a way as to be removable therefrom, the shaft having an inner shaft and a tubular shaft which surrounds the inner shaft and which is longitudinally displaceable relative thereto, the tool being locked on the shaft when the tubular shaft is in a locking position and being removable from the shaft when the tubular shaft is in a release position.
Such an instrument is known from DE-C-198 15 228.
An instrument of the type mentioned at the outset is used for surgical interventions on the human or animal body, in particular in the context of minimally invasive surgery.
Depending on the function and design of the tool arranged at the distal end of the shaft, the instrument can be a cutting instrument, a gripping instrument and/or a coagulating instrument, to mention some examples. In the case of a cutting instrument, the tool can be designed as a blade or in the form of two jaw parts which interact to cut in the manner of scissors. In the case of a coagulating instrument, the tool can be designed as an electrode which can be acted upon with high-frequency current from the proximal end of the instrument. The present invention can be used with all the aforementioned instrument types and also with other instrument types, such as needle holders.
Whereas the tool in conventional instruments was connected securely to the distal end of the shaft and could be removed from the shaft for cleaning purposes only by completely disassembling the instrument, the aforementioned DE-C-198 15 228 discloses an instrument in which the tool at the distal end of the shaft can be removed without the instrument having to be disassembled for this purpose.
In this known instrument, the tool is an electrode tip for cutting and coagulating tissues by means of high-frequency current. The electrode tip is held exchangeably on the shaft, said shaft having an inner shaft and a tubular shaft which surrounds the inner shaft and which is longitudinally displaceable relative to the inner shaft. The electrode tip is held on the inner shaft, said inner shaft having fixing portions which can be moved radially outward and which release the electrode tip holder inserted into the inner shaft in its outwardly moved release position, and, by contrast, fix it axially in an inwardly moved locking position. The tubular shaft covers the fixing portions in a pushed-forward locking position and releases the fixing portions in a retracted release position.
A comparable instrument with a removable tool at the distal end of the shaft is known from DE-C-43 41 735, this known instrument having, as its tool, two jaw parts which can move relative to one another and which can be actuated, via a power transmission element, by means of a handle at the proximal end of the shaft. The power transmission element in this case extends right through the inner shaft. A design of the medical instrument mentioned at the outset with a power transmission element movable longitudinally in the inner shaft for moving the tool is also possible in the context of the present invention.
The advantage of a medical instrument with a removable tool lies in the fact that different tools can be interchanged during an operation performed with the instrument. In this way, it is no longer necessary to have several complete instruments ready to hand, but only different tools, which can then be interchanged as desired. In the case where the tool is an electrode, it is possible for example to use different tools with different electrode shapes. Such an instrument can thus be used in a more universal manner compared to conventional instruments.
In order to gain acceptance for a medical instrument in which the tool can be removed from the shaft and can be replaced with other tools, in contrast to conventional instruments which have no removable tool, it is necessary to ensure that the handling of the instrument when changing the tool is simple and that the tool change can be done quickly and efficiently.
In the instrument known from DE-C-198 15 228 mentioned above, it has been proposed to simplify handling by designing the tubular shaft so that, in the pushed-forward locking position, it can be rotated about the longitudinal axis of the inner shaft into a position in which it is fixed in the longitudinal direction by a bayonet-like lock on the inner shaft. To remove the tool from the distal end of the shaft, the tubular shaft must be pulled back by hand by means of two grip parts, one of which is connected to the tubular shaft, being turned about the longitudinal axis of the inner shaft in such a way that a pin of the bayonet-like lock engages in a longitudinal groove of the bayonet, after which the tubular shaft can be pulled back by hand.
A disadvantage of this actuating mechanism of the known instrument is that the tubular shaft has to be turned and pulled back relative to the inner shaft by hand. This construction of the actuating mechanism thus requires two-handed operation; one-handed operation is at any rate difficult.
The object of the invention is therefore to develop a medical instrument of the type mentioned at the outset in such a way that the handling involved in removing or applying the tool at the distal end of the shaft is further simplified.